It DOES Need to be that big, I went through several weeks of testing with ALL the available 2 and 3 wire solenoids (About 6 at that time) trying various switch transistors and capacitor values and some more time getting the best relay (Omron DPDT 10A contacts 12V coil), The Best relay is the one that works right for the right number of cycles for the least money. 3300uF would work up to about 100 meters of wire 4700 would work 300 meters of wire and this was @ 12V Dc from an SLA Yuasa NP1.2-12 battery. If you use the 9V battery's make sure the resistor between the battery and the capacitor is just large enough to recharge the capacitor within your control cycle. Typical operation of the 9V devices was twice a day 4 or 5 days a week for 6 month's. If I had it to do over again I'd probably use 2 Gates SLA cells @ 2V2/cell and use a boost mode inverter to charge the cap just prior to use... As a matter of fact one could use 3 D cells ans do quite nicely with a 1A switcher built on a 2.5cm bit of PC board material. Food for thought?

Doc

--> WA7EMS "The solution of every problem is another problem." -Johann Wolfgang von GoetheI do answer technical questions PM'd to me with whatever is in my clipboard

No I've enclosed a data sheet for the MMBT2907 and although the Ic for both the leadded part and the SMT part are the same the Pd of the MMBT part is only 325 mW. there are some high gain non darlington devices made by Zetex that would work better. Choose one in a TO-223 or bigger package. You might also consider andding add a snubber across the coil, I used a 330nF capacitor in series with a 4R7 ohm resistor. The Snubber's purpose is to safely absorb both the positive and negative spikes created when the magnetic field in the solenoid collapses. The field will return about 90% of the energy put into it and it will wing several hundred volts negative them about 1/3 of that back positive so use a high voltage transistor capable of at least 2 watts (the TO-39 case is preferred the TO-18 is IMO too Small and again IMO the TO-39 is ok for 300 mA and the TO-18 100 mA) You Might also consider a Pch Mosfet with a < 1 ohm Rdson in an SO-8 or SOT-223 style case. Post your final circuit. before you start to commit to board. Perhaps you might get some advice that you can use to insure your design is as good as it can be, many of us here have some to a lot of experience in this area...

No THAT WON'T WORK. It Might not self destruct but it certainly wot work as you really wan't. The only thing that keeps both transistors from destruction is the value of the NPN base resistor it prevents the PNP from drawing enough base current to destroy irself. You are missing the base current limiting resistor for the PNP transistor and the base resistor for the NPN is too big by 2 orders of magnitude. Make the PNP base resistor 470R leave the 10K in place and change the NPN base resistor to 1K. You may very well have problems with the PNP as It is really the wrong package and device, read my previous post carefully. I gave you the results of 6 month's of research and experimentation with both 2 wire and 3 wire solenoids.

Doc

--> WA7EMS "The solution of every problem is another problem." -Johann Wolfgang von GoetheI do answer technical questions PM'd to me with whatever is in my clipboard

Yes, I've used the '851 and it is a good device and the best of the three. The drivers I used (a GE D44H11 PNP and a PN222 Mosfet) were used with a relay to reverse or select the right coil (for 3 wire solenoids) and were capable of driving any manufacturers solenoids (there were 6 or 7 when I did this work) and would drive the solenoids through 600 meters (1800 Ft) of wire, we guaranteed 300 meters of 16 Ga wire would operate any solenoid. Test it carefully and If you have issues with the driver let me know and I will do what I can to make it work for you.I need to apologize for a misleading statement. I have never used the Zetex part to control a solenoid. I have used the Zetex part for power control and the '851 is a serious high gain power transistor in a strange TO-92? type of plastic case.

Doc{{Edit RKJ}

--> WA7EMS "The solution of every problem is another problem." -Johann Wolfgang von GoetheI do answer technical questions PM'd to me with whatever is in my clipboard

That Sir is what I was trying to tell you. 1. 1 solenoid only per controller 2. the transistors must be capable of 20A surge current for about 50 uS I used 2 different ones a D44H11 PNP and a PN222 Mosfet I found surplus somewhere. It wasn't the best part but it was OK for the design And the surplus guy had about 5K of them that He'd be happy to get $0.05 Ea for.. So I used the Rdson to damp the solenoid by keeping the gate high (or base low) this kept the 4700 uF cap connected until all the ringing stopped, 100 mS worked well. I used a 100 ohm resistor in series with the cap and the battery to make it the capacitor the only source of current... A battery dies after a while and it does so generally by loosing current capacity, the capacitor means that as long as the battery/solar panel can keep the cap charged all will work as it should even with a battery reduced to 100 mAH capacity. I was using 1.2 AH Yuasa 12 V SLA batteries. The charging was processor controlled and temp compensated charge rates were applied to avoid battery damage due to overcharging. Controlling a bi-polar solenoid is easy but it takes some seriously wide PCB tracks and a serious driver transistor, a very serious driver. Probably the easiest for you would be an H-Bridge based on an L298 H bridge motor driver, 2 pulses Forward (open) and Go (momentarily apply power) and 2 more for the Reverse (close) and Go. The shields are 6 to 12 dollars each and ready for your application assuming that your original spec's were right. You could charge a capacitor and "dump" it into a coil with the H-Bridge.

Bob

--> WA7EMS "The solution of every problem is another problem." -Johann Wolfgang von GoetheI do answer technical questions PM'd to me with whatever is in my clipboard